By Sid Perkins
A recent survey along a midocean ridge beneath the Arctic icepack unveiled an unexpected abundance of hydrothermal activity. Besides casting doubt on current theories about where such vent systems can arise, the wayward vents could harbor ecosystems that are dramatically different from those found in other oceans.
Midocean ridges are seams where material wells up from Earth’s interior to form new seafloor, explains Hedy Edmonds, a marine geochemist at the University of Texas’ Marine Science Institute in Port Aransas. In 2001, she and other scientists used icebreakers to plow their way across the Arctic Ocean to make measurements along a 1,100-kilometer segment of the 1,800-km-long Gakkel Ridge. That little-explored midocean ridge, which is spreading slower than other known seams, runs within 350 km of the North Pole and lies at frigid depths between 4,500 and 5,000 meters.
Edmonds and her colleagues dredged the ocean floor for rocks at more than 150 sites along the ridge. As the dredge dropped to the seafloor, instruments attached to its cable measured the temperature and optical properties of the seawater. That’s when evidence for vents started pouring in. At 119 sites, researchers found thick layers of water with high concentrations of suspended particles. At 58 of those spots, those light-scattering layers were warmer than those above and below. Water from some sites contained manganese, often a component of the mineral-rich water discharged from vents. The data suggest there are 9 to 12 vent systems along the surveyed segment.
Until recently, most scientists thought the amount of hydrothermal activity along a particular portion of a midocean ridge depended on the rate of seafloor spreading there, says Edmonds. Her team’s survey, described in the Jan. 16 Nature, found double to triple the number of vent systems that current models predict.
The newfound vents may soon catch biologists’ attention. Hydrothermal vents often host thriving ecosystems that are nourished by the warm, mineral-rich fluids. The biological communities that surround the Gakkel Ridge’s vents may be significantly different from those that populate hydrothermal systems elsewhere, says Cindy L. Van Dover, a biological oceanographer at the College of William and Mary in Williamsburg, Va. Deep parts of the Arctic Ocean contain many unique aquatic species, she notes.
“I’d say that Arctic hydrothermal vents are the premier sites for finding new species,” says Van Dover.
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